Increasing attention has been focused on emergency telephone services (911) in the past several years because, as more and larger communities are served by 911 service, certain limitations have received publicity. Initially, 911 systems relied on interaction between the caller and the operator at the PSAP to identify the location of the caller. Thus the operator could not obtain accurate location information if the caller were a child, were incapacitated, or hung up the telephone before the location was given.
More recently, certain location information of the originating telephone became available automatically as the call was being established. As the call is set up through the network, the automatic Number Identification (ANI) used for establishing long distance calls is delivered to the PSAP. A database query is then dispatched to obtain location information of the caller, based on the ANI of the telephone from which the call is originating. For most residential telephones, this is sufficient data to determine location. However, for businesses, such as large office complexes, this data is not sufficient to locate the office or area where the call is being made. The reason that some location information can be incomplete or misleading is that ANI is the billing number of the calling telephone, not the directory number of that telephone. It would be preferable to know the directory number of the calling party, but the telephone network cannot transmit the directory number of the calling party to existing PSAPs.
In order to understand this problem, it is helpful to understand the current state of the art of 911 systems. FIG. 1 is a block diagram of a prior art 911 system 100. 911 system 100 generally comprises a switching system 102 connected via a trunk group 104 to a public safety answering point (PSAP) 106. Switching system 102 is called the 911 tandem because it routes calls from a 911 service region 108 to the PSAP 106 serving that region and may comprise any type of switch that can route calls over trunks. 911 tandem 102 services individual lines such as 110 and 112, lines from other switches, such as line 114 connected to switch 116, and lines from other equipment, such as private branch exchanges 118 and 120. When switch 116 receives a 911 call from line 114, for example, switch 116 routes the 911 call to 911 tandem 102, passing the ANI. 911 tandem 102 then identifies which PSAP handles calls from that ANI, and translates the PSAP identification into a route index. 911 tandem 102 routes the call according to the route index over trunk group 104 to PSAP 106.
PSAP 106 includes trunk to line conversion hardware 122 to terminate trunk group 104 and convert the trunks into line appearances. Connected to trunk to line conversion hardware 122 is a key system 124 to provide connections between incoming 911 calls and operator positions 126-128 at PSAP 106. Key system 124 alerts every telephone attached to it, as is known in the art. An automatic number identification (ANI) converter 130 connected to trunk to line conversion hardware 122 receives the incoming ANI from the trunk and displays it to the operator. Trunk-to-line conversion hardware 122 uses the ANI to cause a query to be sent to an automatic location identification (ALI) system 132. ALI system 132 is a database which receives the incoming ANI directory number and provides name, address, type of service (business, residential, etc.), and other information (such as special needs or hazards) associated with the directory number. ALI system 132 is connected to the trunk termination equipment via a dedicated link 134.
When a 911 call is made from a residential telephone, such as telephone 110, 911 tandem office 102 routes the call to PSAP 106. The call is routed over trunk group 104, and the call set up protocol includes sending the ANI associated with telephone 110 to PSAP 106. In PSAP 106, the trunk to line conversion hardware 122 receives the call and alerts key system 124, which in turn alerts every operator position 126-128 in PSAP until one of the operators answers the call. The ANI of telephone 110 is displayed on converter 130, and the trunk-to-line conversion equipment 122 causes an ALI query to retrieve the location information for telephone 110. The operator may then initiate other calls to the appropriate public safety departments.
This system works relatively well for a call from a telephone located in a residence, but has several limitations for businesses with multiple telephones. As stated above, ANI is the billing directory number of the subscriber, and not necessarily the directory number (herein referred to as "calling party number" or "CPN") of any specific telephone, but is used primarily to provide an address for billing purposes. If the 911 call is from a telephone at a large business campus, it is likely to originate over a PBX, such as 120. The call is routed by PBX 120 over trunks 136 to switch 116, which in turn routes the call over trunks 138 to 911 tandem office 102. The ANI of the PBX trunk 136 is delivered to the 911 tandem office 102 as part of call set up. 911 tandem office 102 routes the call to PSAP 106, and as before, the call is presented to the operators and an ALI query is dispatched to ALI system 132. However, since the only telephone number that is received is the ANI, only the location of the billing number is displayed. The actual location of the telephone from which the 911 call originated is not generally available to the operator. This has proven in the past to cause delays in locating the person who made the call, sometimes with fatal consequences.
Some PBX systems (such as an AT&T Definity.RTM. telecommunication system) can send the CPN of the calling telephone to the PSAP today, but only when there are specific connections to the network. These PBX systems send the CPN to the 911 tandem provided that the 911 tandem is a 5ESS.RTM. switch and the PBX system is connected to the 5ESS.RTM. switch by a primary rate interface (PRI) trunk. A PRI is a trunk group comprising a plurality of digital voice channels and a data channel. Special action is taken at the PBX to send the CPN in addition to the ANI to the 5ESS.RTM. switch. The 5ESS.RTM. switch then replaces the ANI with CPN, but only for 911 calls with this specific equipment.
In general, however, current 911 systems are limited in their ability to guide public safety offices to the exact location of an emergency, because of limitations inherent in 911 systems. Additionally, PSAP systems are limited as to what outgoing features may be used from the current key systems. Current 911 systems only permit speed calling, 3-way calling, and selective transfer (transferring the call to another 911 PSAP based on the location of the ANI). Finally, the equipment at these prior art PSAPs is very expensive for local governments to purchase, maintain, and install, because of the specialized nature of the equipment. 911 trunk to line conversion hardware is used only in PSAP systems, and the key system is used as operator services equipment.
Therefore, a problem in the art is that there is no 911 system that can provide CPN for both residences and businesses, provide a greater number of features, and be low in cost.